Schmalfeld et al in U.S. Pat. No. 3,926,576 discloses briquettes having improved crushing strength which are made from hot coke containing mixtures at temperatures between 350.degree. to 550.degree. C. These briquettes are made by admixing tar pitch with hot coke and then pressure forming the briquettes, for example on a double roll press. In Example 3, Schmalfeld et al disclosed that the strength of the cooled briquettes was increased to 161 kilograms per square centrimeter.
Mansfield et al in U.S. Pat. No. 3,969,088 discloses raw coal being charred in pre and post treatment carbonizers, then pulverized, mixed with pitch, briquetted, re-circulated through the pre and post treatment carbonizers with succeeding green coal, cooled, and finely separated from the as yet unbriquetted char.
Mikhailovich Grechanichenko et al in U.S. Pat. No. 3,856,481 disclosed a method of making plastic coal briquettes wherein initial coal is heated up to a softening temperature and subsequently cured under approximately isothermal conditions. Pressure forming is then effective in two stages. During the first stage, a coal strip of which the thickness is not less than the required thickness of a final product, i.e. of a briquette is pressure formed while during the second pressure forming stage plastic coal briquettes are produced from this strip.
Elliott, Chemistry of Coal Utilization, Second Supplementary Volume, 1981, pages 633-638, discloses a coking process wherein brown coal is dried, low temperature carbonized, cooled, comminuted, mixed with tar and additives briquetted and coked. Brown coal is a non-caking coal which do not have a softening point. The coke briquettes of Elliott is not a blast furnace quality high strength product.